1. Technical Field
The invention is related to face recognition systems for identifying people depicted in an input image, and more particularly to such a face recognition system and process that also identifies the face pose of each identified person.
2. Background Art
The problem of recognizing people depicted in an image from the appearance of their face has been studied for many years. Face recognition systems and processes essentially operate by comparing some type of model image of a person's face (or representation thereof) to an image or representation of the person's face extracted from an input image. In the past, most of these systems required that both the original model image and the input image be essentially frontal views of the person. This is limiting in that to obtain the input images containing the a frontal view of the face of the person being identified, that person had to either be purposefully positioned in front of a camera, or a frontal view had to be found and extracted from a non-staged input image (assuming such a frontal view exist in the image).
More recently there have been attempts to build a face recognition system that works with faces rotated out of plane. For example, one approach for recognizing faces under varying poses is the Active Appearance Model proposed by Cootes et al. [3], which deforms a generic 3-D face model to fit the input image and uses the control parameters as a feature fed to a classifier. Another approach is based on transforming an input image into stored prototypical faces and then using direct template matching to recognize the person whose face is depicted in the input image. This method is explored in the papers by Beymer [4], Poggio [5] and Vetter [6].
Essentially, all the current face recognition approaches can be classified into two categories: model based and appearance based [1]. The model based approach tries to extract geometrical measurements of certain facial parts, while the appearance based approach usually employs eigenfaces [2] to decompose images and then uses decomposition coefficients as the input to a classifier.
The present pose-adaptive face recognition system and process represents an extension of the appearance based approaches and has the capability to recognizing faces under varying poses.
It is noted that in the preceding paragraphs, as well as in the remainder of this specification, the description refers to various individual publications identified by a numeric designator contained within a pair of brackets. For example, such a reference may be identified by reciting, “reference [1]” or simply “[1]”. Multiple references will be identified by a pair of brackets containing more than one designator, for example, [13, 14]. A listing of the publications corresponding to each designator can be found at the end of the Detailed Description section.